(1) Field of the Invention
This invention relates to an exhaust gas treatment apparatus for a working machine such as a hydraulic excavator which enables a specific process in an exhaust gas treatment section to be carried out, by raising the output of an engine by increasing the hydraulic load on the working machine that is hydraulically driven.
(2) Description of the Related Art
FIG. 5 is a circuit diagram showing an example of an exhaust gas treatment apparatus for a working machine according to the related art.
In the related art, working machines such as a hydraulic excavator are provided with an exhaust gas treatment apparatus that treats exhaust gas emitted from an engine and then emits the treated exhaust gas to the outside. As shown in FIG. 5, for example, this exhaust gas treatment apparatus includes a hydraulic pump 8 driven by an engine 5a, an actuator 4a that is actuated upon supply of pressure oil from the hydraulic pump 8, a directional control valve 14 that controls the flow of pressure oil supplied to the actuator 4a, and an operating device 19 having an operating lever 19a operated to switch the directional control valve 14.
The exhaust gas treatment apparatus also includes a pilot pump 16 that supplies pressure oil to the operating device 19, an open/close valve 13 that is arranged downstream of the directional control valve 14, and controls the opening and closing of a channel connected to a tank 25, a control valve 15 that is arranged between the open/close valve 13 and the pilot pump 16, and controls the open/close valve 13 to an open position 13a or a close position 13b, and a lock valve 17 that is arranged between the pilot pump 16 and the operating device 19, and can be switched between a lock position 17c for keeping actuation of the actuator 4a disabled, and an unlock position 17b for enabling actuation of the actuator 4a. It should be noted that the hydraulic pump 8, the pilot pump 16, and the lock valve 17 are each connected to the tank 25. A relief valve 20 is provided in a pipe 26 connecting between the pilot pump 16 and the lock valve 17. When the pilot pressure oil supplied from the pilot pump 16 becomes excessive, the relief valve 20 relieves the excess pilot pressure oil to the tank 25.
Further, the exhaust gas treatment apparatus includes an exhaust gas treatment section 11 that is attached to the exhaust port 10 of the engine 5a, and treats exhaust gas emitted from the engine 5a, a detecting section 12 that detects when a specific process that raises the exhaust temperature of the exhaust gas treatment section 11 becomes necessary, and outputs a signal for setting the control valve 15 to an open position 15b, and a controller 18 that controls the control valve 15.
Specifically, the exhaust gas treatment section 11 has in the inside a filter (not shown) with an oxidation catalyst such as platinum. By capturing and oxidizing unburned matter such as carbon hydride or carbon monoxide in exhaust gas with the filter, the exhaust gas treatment section 11 changes the unburned matter into harmless matter such as water or carbon dioxide and then emits the harmless matter. At this time, the oxidation catalyst such as platinum provided in the filter does not exert an effective catalytic effect unless its temperature becomes equal to or higher than a predetermined temperature specific to the oxidation catalyst. Accordingly, if the temperature of exhaust gas flowing into the exhaust gas treatment section 11 is lower than this specific predetermined temperature, the captured unburned matter builds up on the filter without being oxidized. As a result, the emission efficiency of exhaust gas in the exhaust gas treatment section 11 deteriorates, resulting in increased exhaust resistance for the engine 5a. To prevent this, in the related art, it is common to perform a specific process that raises the exhaust temperature of the exhaust gas treatment section 11 by raising the temperature of exhaust gas emitted from the engine 5a. The detecting section 12 includes an exhaust pressure sensor that detects the pressure of exhaust gas flowing into the exhaust gas treatment section 11, and also a temperature sensor that detects the temperature of exhaust gas. When the detecting section 12 detects by the exhaust pressure sensor that the pressure on the upstream side of the oxidation catalyst has become high, and also exhaust temperature is low, the detecting section 12 outputs a signal indicating the start of the above-mentioned specific process.
As an example of an exhaust gas treatment apparatus for a working machine which performs such a specific process, there exists a hydraulic working machine in which the detecting section 12 is provided on the inlet side of an exhaust gas control device provided in a connected fashion to the exhaust port 10 of the engine 5a, in other words, the exhaust gas treatment section 11, and detects the exhaust resistance of the engine 5a, and further, in which the controller 18 includes the function of raising the discharge rate and discharge pressure of pressure oil discharged from the hydraulic pump 8, in other words, raising the output of the engine 5a when the exhaust resistance measured by the detecting section 12 becomes a predetermined preset value or more, thereby raising the temperature of exhaust gas from the engine 5a to a sufficient temperature for enabling the exhaust gas treatment section 11 to exert its exhaust gas treatment capability properly (see, for example, Japanese Patent No. 3073380).
As shown in FIG. 5, in the hydraulic working machine disclosed in Japanese Patent No. 3073380, the operating lever 19a of the operating device 19 is attached with a neutral detection switch 19b for detecting the neutral state of the directional control valve 14. The neutral state of the directional control valve 14 is electrically detected by closing of the circuit of the neutral detection switch 19b, and the above-mentioned specific process is performed only when the directional control valve 14 is in the neutral state, thereby preventing the actuator 4a from operating in a manner not intended by the operator.
In other words, as shown in FIG. 5, when the controller 18 receives a signal indicating the neutral state of the directional control valve 14 on the basis of the neutral detection switch 19b, and the exhaust resistance measured by the detecting section 12 becomes equal to or higher than a predetermined preset value, the controller 18 switches the control valve 15 to the open position 15b that is the upper position, thereby causing the pilot pressure oil from the pilot pump 16 to be supplied to a control part on the right side of the open/close valve 13 via the control valve 15. Thus, the open/close valve 13 is switched to the close position 13b that is the right position. Then, the pipe line leading to the tank 25 is closed, and the discharge pressure of the pressure oil discharged from the hydraulic pump 8 rises simultaneously. This prevents an increased amount of pressure oil being supplied from the hydraulic pump 8 to the actuator 4a due to the specific process while the operator is operating the operating lever 19a of the operating device 19. In other words, operation of the actuator 4a in a manner not intended by the operator is prevented, thus allowing work to be done safely.